PROTEINS CAN BE ATTACHED TO DIAMOND LAYER TO CREATE BIO-SENSORS
16 March 2007 - DOE/Argonne National Laboratory

The research was presented today at the annual meeting of the American Chemical Society in Philadelphia and will appear soon in the journal Langmuir.

Biomolecules can be harnessed for a broad range of uses from detecting anthrax spores to helping diabetics monitor their blood sugar. But to harness the function of biomolecules effectively and prevent them from drifting away from their site of activity, scientists need to precisely immobilize them by attaching them to a firm surface.

Jian Wang, a postdoctorate researcher at Argonne, has developed an innovative way to construct hybrid organic-inorganic interfaces based on conducting diamond thin films. This interface allows biomolecules such as proteins to be anchored to the diamond surface in such a way as to preserve their functionality.

“We developed a very thin diamond layer we call ultrananocrystalline diamond, which can be doped with nitrogen and made very highly electrically conductive,” he said. “We immerse the UNCD into a special solution and apply voltages, which creates radicals that react with the diamond surface to form strong carbon-carbon bonds.” This attached organic layer establishes an anchor to which biomolecules such as proteins can be covalently bound in a process called functionalization.

"This is revolutionary,” said Argonne physicist John Carlisle. “The UNCD grain size is three to five nanometers, which is only 20 carbon atoms in diameter.” Nanometers are extraordinarily small, one nanometer is one-billionth of a meter, and is thousands of times smaller than the period at the end of this sentence. Devices at the nanometer size are so small that they cannot be seen without a microscope.

“Now that we can immobilize specific molecules on electrochemically active UNCD surfaces," Carlisle said, "we can use them for all sorts of things, such as to detect the presence of bio-terrorist chemicals like anthrax or sarin, or in artificial retinal implants. We can also integrate these functionalized UNCD surfaces into microelectromechanical systems devices to make biosensors.”

The scientists' challenge was to modify the ultra-thin diamond surface so bio-molecules could ultimately adhere to it, without changing UNCD's otherwise favorable biomaterial properties. Diamond is an ideal interface because it forms carbon-carbon bonds, among the strongest chemical bonds, and it is durable. Diamond is also chemically inert so it does not cross-react with the proteins.

Once the UNCD is functionalized with organic molecules as an anchor, the researchers can attach other biomolecules to them for uses such as bio-sensing.

“Suppose you want to detect the presence of anthrax,” said Carlisle. “First you take a protein that fits an anthrax spore protein in the classic lock-and-key model. That protein acts as a probe, so when an anthrax protein binds to it, it initiates an interaction that confirms the presence of the spore.” Similar models could lead to the detection of many chemicals, including other biowarfare agents.

The Argonne researchers actually “grow” the ultrananocrystalline diamond in the laboratory. They begin with a gas mixture that is one percent methane and 99 percent argon gas, and excite it in a microwave plasma reactor. The result is a plasma composed of many forms of carbon-containing molecules, including hydrocarbons and C2 dimers.

Dimers are compounds made up of two different molecules of the same substance.When these molecules are exposed to diamond nanocrystals, they bind with them as diamond themselves, “growing” the diamond surface.

UNCD is finding many applications in addition to biosensors, including electronics, wear-resistance coatings, flat-panel displays, and artificial retinas. A start-up company, Advanced Diamond Technologies, Inc. has been created by Argonne to commercialize this material.

Other Argonne collaborators are Millicent A. Firestone and Orlando Auciello. The research was supported by the Department of Energy's Office of Science, and Argonne's Strategic Laboratory Directed Researchand Development Programs in Nanoscience and National Security.

The nation's first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Since 1990, Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

http://www.anl.gov

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